Measuring index of machine tools

he quality of the machine tool directly affects the quality of the machine. Measuring the quality of a machine tool is multifaceted, but the main requirements are good workmanship, serialization, generalization, high degree of standardization, simple structure, light weight, reliable work, high productivity. The specific indicators are as follows:


1. Possibility of process


The possibility of technology refers to the ability of machine tools to adapt to different production requirements. Universal machine tools can complete a certain range of parts within a certain size of multi-process processing, the possibility of technology is wide, so the structure is relatively complex, suitable for single piece of small batch production. The special machine tool can only complete one or several parts of a specific process, the possibility of its process is narrow, suitable for mass production, can improve productivity, ensure processing quality, simplify the structure of the machine tool, reduce the cost of machine tools.


2. Accuracy and surface roughness.


In order to ensure the accuracy and surface roughness of the machined parts, the machine itself must have certain geometric accuracy, kinematic accuracy, transmission accuracy and dynamic accuracy.


Geometric precision refers to the accuracy of mutual position between parts and the shape and position accuracy of main parts when the machine tool is not running. Geometric accuracy of machine tools has an important impact on machining accuracy, so it is the main index to evaluate the accuracy of machine tools.


Motion precision refers to the geometric position accuracy of the main parts when the machine tool is running at the working speed. The greater the change of geometric position, the lower the motion accuracy.


Transmission accuracy refers to the coordination and uniformity of the movement between the ends of the transmission chain of machine tools.


The above three precision indicators are tested under the condition of no-load. In order to fully reflect the performance of the machine tool, it is necessary to require the machine tool to have a certain dynamic accuracy and the shape and position accuracy of the main parts under the action of temperature rise. The main factors affecting dynamic accuracy are stiffness, vibration resistance and thermal deformation of organic beds.


The stiffness of the machine tool refers to the ability of the machine tool to resist deformation under the external force. The greater the stiffness of the machine tool, the higher the dynamic accuracy. Stiffness of machine tools includes stiffness of machine parts and contact stiffness between components. The stiffness of machine tool components mainly depends on the material properties, section shape and size of the components themselves. The contact stiffness between components is not only related to the contact material, the geometric dimension and hardness of the contact surface, but also to the surface roughness, geometric accuracy, machining method, contact surface medium, pre-pressure and other factors.


Vibration on machine tools can be divided into forced vibration and self excited vibration. Self-excited vibration is a kind of continuous vibration generated by the cutting process without any external force and exciting force. Under the continuous action of the exciting force, the forced vibration of the system is forced vibration.


The aseismic property of machine tools is related to stiffness, damping characteristics and quality of machine tools. Because the thermal expansion coefficient of each part of the machine tool is different, the deformation and relative displacement of each part of the machine tool are different. This phenomenon is called thermal deformation of the machine tool. The maximum error due to thermal deformation can account for 70% of the total error.


There is no unified standard for the dynamic accuracy of machine tools. The dynamic accuracy of machine tools is evaluated indirectly by the accuracy achieved by cutting typical parts.


3. Serialization and so on


Serialization, generalization and standardization of machine tools are closely related. Variety serialization is the basis of generalization and standardization of parts, while generalization and standardization of parts promote and promote variety serialization.


4. The life of machine tools


The reliability and wear resistance of machine tool structure are the main indexes to measure the service life of machine tools.